Both silicone and organic polymers which contain reactive functional groups are known in the art. Of commercial interest are polyisobutylene (PIB) systems containing hydrolyzable silyl groups since they can be used to formulate moisture-curable sealants, caulks and adhesives, inter alia. Unlike the well known moisture-curable silicone room temperature vulcanizable (RTV) compositions, systems based on polymers having a PIB backbone offer the advantage of low permeability, making them eminently suitable for gas barrier applications such as formed-in-place gaskets, O-rings, rubber plugs/seals, and the like. In these PIB polymers it is particularly desirable that the functional groups reside at each end of the molecular chain. Such telechelic polymers offer an advantage in that the molecular weight between reactive groups can be controlled. Consequently, when a telechelic polymer is cured, the molecular weight between crosslinks (i.e., the network structure) and, therefore, ultimate mechanical properties of the product, can be controlled and essentially no "dangling" ends remain.
For example, U.S. Pat. No. 4,904,732 to Iwahara et al. discloses, inter alia, the preparation of a silyl-functional PIB polymer by hydrosilating a corresponding polymer which contains unsaturated groups. The resulting polymer can have an essentially telechelic structure and can be cured (e.g., by exposure to moisture). However, the total process suggested by Iwahara et al. is quite complicated and, therefore, expensive.
Using a different approach, U.S. Pat. No. 4,829,130 to Licchelli et al. discloses a method for preparing silylated copolymers of isobutylene which are crosslinkable upon exposure to moisture. In this case, isobutylene is copolymerized with a comonomer having a vinylic group attached to a silylalkyl group through a benzene ring connecting group. Ostensibly, the product of this statistical copolymerization is a polyisobutylene having pendant silyl-functional groups along its main chain and, although the process is relatively uncomplicated, the location of functional groups can not be controlled and the products are inherently inferior to silyl functional telechelic polymers.
Likewise, U.S. Pat. No. 4,524,187 to Greco et al. teaches crosslinkable polyisobutylene copolymers having pendant silyl functionality. In this case, isobutylene is first reacted with a triene compound to form a copolymer having pendant vinyl groups, the latter then being silylated with a moisture-reactive hydridosilane or mercapto-functional silane. Again, control of functional group distribution is not possible.
Thus, there is still a need for simpler means of synthesizing a silyl-functional polyisobutylene which can be readily cured by exposure to moisture to form a crosslinked elastomer having properties which approach those of the corresponding telechelic system.